One common theme is the balance between life and death. Xerneas represents life with its life - giving abilities, and Yveltal represents destruction or death. Fanfics often explore how these two forces interact and keep a balance in the Pokemon universe.
The plot is crucial. It could be a story about the struggle between Xerneas and Yveltal's opposing powers and how Zygarde tries to maintain the balance. Or perhaps a story where the trainer has to deal with the consequences of the actions of these powerful Pokemon. A plot that keeps you on your toes and makes you want to keep reading is a sign of a great fanfic.
One idea could be a story where Yveltal and Xerneas are forced to team up to face a new, greater threat that endangers their entire Pokemon world. Maybe a powerful and evil force is spreading chaos and they realize they can't defeat it alone.
You can start by looking on fanfiction websites like FanFiction.net or Archive of Our Own. There are often many talented writers who create stories about these Pokemon. Just search for 'Xerneas Yveltal Zygarde fanfic' in the search bar, and you'll get a list of relevant stories.
There's also a fanfic called 'Xerneas' Glow and Yveltal's Shadow'. In this story, it delves into the symbolic meaning of Xerneas' life - giving light and Yveltal's more destructive nature. It has an interesting plot that unfolds as the two Pokemon cross paths in a series of adventures.
One idea could be a story where Xerneas and Yveltal have to team up to save the Pokemon world from a new, unknown threat. They have different powers and personalities, so it would be full of conflict and cooperation.
Xerneas, on the other hand, is all about rejuvenation. Its power can be shown as a bright, glowing light that spreads across the land. If a barren field is in the path of Xerneas' power, it will soon be filled with lush grass and blooming flowers. In a fanfiction, a character who is injured or sick might be healed by just being near Xerneas.
Weakness was a movie about the challenges and difficulties faced by boxer Jack Sully in his career, as well as his discovery of his weaknesses in matches and training. In the movie, Jack found that his key was his "fear" and "lack of confidence." By overcoming these weaknesses, he eventually became a successful boxer.
Once, I was at a concert. There was a couple in front of me who seemed to be having their own little dance party. They were completely out of sync with the music and each other. The guy was doing some really wild moves, and the girl was trying to be all elegant. It was a strange and funny sight. People around were trying not to laugh out loud, but it was really hard.
My friend and I were hiking in the mountains. We came across a family of deer. One of the fawns was really curious and started following us. It was so cute. We tried to shoo it away gently because we didn't want to disrupt it too much, but it just kept coming closer. Eventually, its mother called it back and we all had a good laugh about our little furry follower.